Japan is, as you may have guessed, a foreign country. Unless you're Japanese.
One aspect of this is that the many of the holidays celebrated may be completely unfamiliar to non-Japanese anime viewers. Further, holidays known to Western culture may have an entirely different spin on them.
Here is a short chronological listing of Japanese holidays, with an eye to those portrayed in various anime. Note that not all are actual holidays in the sense of "days off". Conversely, unlike in the U.S. with its school-on-Columbus-Day shenanigans, if it's a national holiday in Japan (even if it's just the equinox) you get that day off.
- Japanese New Year (Oshogatsu) (January 1-4) - Eating traditional Japanese New Year's foods (osechi) and mochi (rice cakes) is big. Japanese people tend to send postcards for New Years instead of Christmas. Children receive their otoshidama, New Year's money packets. Poetry and games are also traditions, especially in the games of uta-karuta, where poems from the Hyakunin Isshu are used for a snap-style card game, and iroha-karuta, whose cards illustrate topical sayings that form an acrostic for the Japanese syllabary.
- Coming of Age Day (Second Monday of January, January 5 before 2000) - A day to congratulate and encourage people who have reached twenty years (the age of majority) after the previous Coming of Age Day. A kind of Coming of Age celebration.
- Setsubun (February 3) - Not a national holiday, this day traditionally marks the beginning of spring. Throwing beans to ceremonially expel negative spirits from the household is a characteristic tradition. Technically, this is spring Setsubun, properly called Risshun; each seasonal division can be called Setsubun.
- National Foundation Day (February 11) - A celebration of the foundation of Japan and the imperial line by Emperor Jimmu in 660 BCE (Imperial Year 1 or Kōki 1).
- Valentine's Day (February 14) - Not a national holiday, this day is imported by chocolate companies, as a result of which the Japanese version of the holiday centers heavily around chocolate. Women give chocolates to their special men, as well as "obligation chocolate" to their male coworkers. The fact that only men get presents is (according to The Other Wiki) due to a typo made by an ad exec during the original advertising campaign. See White Day below.
- Parinirvana Day (February 15) - Not a national holiday. A Buddhist holiday celebrating the day when the Buddha achieved Parinirvana, celebrated on the day of his death. It is a day for meditation and to reflect on one's own death and the departure of those recently deceased. Passages from the Mahaparinirvana Sutra are often read. It is called Nehan-e in Japanese.
- Emperor's Birthday (February 23) - A celebration of the reigning Emperor's birthday. The date obviously changes when a new Emperor takes the throne, although the Japanese Diet still has to convene to "officially" designate a new date for the holiday.Note
- Doll Festival/Girls' Day (March 3) - Not a national holiday. A traditional day for young girls. Platforms covered in red carpet are set up with a display of dolls representing the Emperor, Empress and their court in Heian period dress along with palace accesories; It's complemented by Children's Day/Boys' Day (See Golden Week below).
- White Day (March 14) - Not a national holiday. On this day, men return the favour shown to them by women on Valentine's Day. Woe betide the anime man who forgets this! Like many "greeting card holidays" in the West, it was largely invented by marketers trying to give people an excuse to buy white chocolate and marshmallow confectionaries.
- Vernal equinox (around March 20) - A day for celebration of spring and admiration of nature.
- Hanamatsuri (April 8) - Not a national holiday. Known as Buddha's Birthday in English, Vesākha in Pāli, and a variety of names in Japanese, this is a Buddhist holiday celebrating the life of Gautama Buddha. In Japan, Buddhists pour ama-cha (hydrangea beverage) over small Buddha statues decorated with flowers. Formerly celebrated 8th day of the 4th month of the Chinese calendar before the Gregorian calendar adoption in the Meiji Restoration.
- Golden Week (April 29-May -5) - A series of holidays clustered together which effectively serve as a whole week long vacation for the work-oriented Japan. This shows up prominently in Japanese popular media, but it is often characterized by virtual gridlock in the otherwise excellent train system, prompting the media to breathlessly report on just how over-capacity the shinkansen is. Also the bane of manga fans, since Shonen Jump always takes the week off. The holidays in question are:
- Showa Day (April 29) - Celebrated for years as the birthday of the Showa Emperor (Hirohito) until his death in 1989. Greenery Day was celebrated in its place until 2007 when it became a day to reflect on the events of the Showa period.
- Constitution Memorial Day (May 3) - Established in 1948 to commemorate the day Japan's postwar constitution was ratified.
- Greenery Day (May 4) - A day to celebrate and be thankful for nature's blessings. It was originally held on April 29 to replace the Emperor's Birthday in the national holidays until Showa Day was established. Greenery Day was then moved to May 4, a day that was already established as a nameless public holiday because it fell between two already established holidays.
- Children's Day (May 5) - A day to celebrate Japan's children. Originally the holiday was just Boy's Day.
- Tanabata (July 7) "The Evening of The Seventh" - Not a national holiday. A holiday with romantic connotations. There is a legend in Asia called "The Weaver and the Cowherd" about two lovers (Orihime and Hikoboshi, who are the stars Vega and Altair) who can meet only once a year and only if it doesn't rain on the seventh day of the seventh month. (More information here on The Other Wiki.) It is marked with festivals and with writing wishes on strips of paper and attaching these to bamboo.
- Marine Day (Third Monday of July) - A day of thanksgiving for the ocean and its bounty which has sustained Japan through the ages.
- Obon (July or August 13-15) - Not a national holiday. A traditional Buddhist celebration aimed at alleviating the loneliness of deceased ancestors. It's often used as a day for family reunions and, since it's during the summer, it often involves outdoor festivals and the wearing of yukata. Buddhists visit and clean the graves of ancestors and the spirits of the dead revisit their household altars. Usually concludes with the floating of paper lanterns down rivers, symbolizing the return of the spirits back to the realm of the dead. Look for the traditional Bon Odori dance.
- Mountain Day (August 11) - A brand new holiday starting in 2016 to allow the Japanese to enjoy and marvel in the nation's mountains, lobbied for by the Japanese Alpine Club. This day was chosen to coincide with the holiday time normally given by employees to participate in Obon.
- Respect-for-the-Aged Day (Third Monday of September) - A day for veneration of elders and celebration of long life.
- Autumnal Equinox (Usually September 23) - A day to remember the deceased and one's ancestors.
- Silver Week (September 18-22 or September 19-23): A very rare occurrence in the Japanese calendar where Respect-for-the-Aged Day is observed the same week as the Autumnal Equinox, such that a citizen's holiday is created between the two, and the previous weekend is included in the time off.
- Tsukimi - Not a national holiday. Harvest moon festivals. The festival for the full moon is fifteenth day of the eigth month of the lunisolar calendar; the thirteenth day of the ninth month is for the waxing moon. These days are typically in September and October in the Gregorian calendar.
- Culture Day (November 3) - A day of promotion of culture celebrated typically with art exhibits and cultural festivals. It falls on the same day as the old holiday that celebrated the birthday of the Meiji Emperor.
- Shichi-Go-San (November 15) - Not a national holiday, so it may be observed on the nearest weekend. It is a rite of passage celebration for seven and three year-old girls and five and three year-old boys, hence its name: Seven-Five-Three. Thousand year candy is given to children on this day.
- Health and Sports Day (Second Monday of October) - A day to celebrate sport and the health of mind and body.
- Halloween (October 31) - Not a national holiday and not highly celebrated; the Buddhist festival Bon may be the closest equivalent of what Halloween once was, since the spirits of the dead revisit household altars. Awareness of Halloween has increased of late as more and more American media makes it to Japan. Tokyo Disneyland in particular has been largely attributed to the rising popularity of the holiday in the country, as they began their own Halloween event in 2000, which quickly became a success. Universal Studios Japan would later further expand the holiday's presence via their own event. Japanese stores took notice of the popularity of the parks' events and began selling a vast array of Halloween merchandise, making things snowball from there. Some anime use Halloween an an excuse to put a cast of cute girls in cute costumes. Generally there are a lot of (cute, not scary) Halloween decorations about for the month of October, but unlike elsewhere in the world, trick-or-treating is not commonly done during the holiday — it is rather instead seen as a time for people to dress up and go to parties.
- Labour Thanksgiving Day (November 23) - A celebration of labour and production equivalent to May Day or Labour Day celebrated elsewhere on May 1. (May Day is also celebrated by some trade unions in Japan).
- Bodhi Day (December 8) - Not a national holiday. A minor Buddhist holiday in Japan commemorating the Buddha's achievement of englightenment, like Vesākha/Hanamatsuri, which is a more widely celebrated occasion. Zen Buddhists call it Rohatsu; Tendai Buddhists call it Shaka-Jōdō-e. Traditions for its celebration vary between sects.
- Christmas Eve and Christmas (December 24-25) - Not a national holiday. In Japan, Christmas is considered a romantic holiday, to be spent with one's love rather than family (that is usually for New Years). This event is often a plotline in any anime featuring romance or romantic relationships. It is also celebrated in a more secular manner. In postwar Japan, KFC jumped on an opportunity to corner the market and made fried chicken a staple of Japanese Christmas dinner, with people pre-ordering buckets a month in advance; this explains why Colonel Sanders may be considered interchangeable with Santa Claus in Japanese media.
- Omisoka (December 31) - Not a national holiday, but New Year's Eve and the preparations in the week leading up to it are almost as important as New Year's Day itself and the period could be considered one "holiday" for the purposes of how it is portrayed. "Forget-the-year" parties are big at companies, and may involve drinking. A thorough house cleaning is often done. Special noodles are served on Omisoka itself. At midnight, a gong is rung 108 times.
If any holiday with a permanent date falls on a Sunday, the following Monday is a "Compensation Holiday" to allow workers to still have the day off as they would have prior. Golden Week has been particularly subject to this, with 2012 through 2015 having April 30 or May 6 observed as time off.
Chinese New Year was once widely celebrated in Japan, but became rare after the Gregorian Calendar was adopted in 1873 to replace the Chinese-based lunisolar calendar. Chinese New Year may still be celebrated by Chinese and Koreans and their descendents in Japan, as well as Okinawa Prefecture which has stronger cultural ties to China. Okinawa also observes Irei no Hi (commonly translated "Okinawa Memorial Day") on June 23 to memorialize the lives lost as a result of the Battle of Okinawa. There are also hundreds of local matsuri (festivals) throughout the country throughout the year.
There are also several special "memorial" or "observance" days that play off alternate Japanese pronunciations of the numerical date's numbers, often promoted by various businesses or clubs in Japan. February 9 (or alternatively any 29th of the month) is "Meat Day" because "2 9" can be read as "niku" ("meat"), so supermarkets and restaurants try to push meat-related sales. August 7 is "celebrated" as "Banana Day" because 8 for August can be pronounced "ba" and 7 as "nana" because the Japan Banana Importers Association deemed it so. Similarly, Japanese confectionary giant Glico declared November 11 as "Pocky & Pretz Day" because 11/11 looks like their Pocky and Pretz snacks.
For context, it should also be noted that certain days are not holidays in Japan. Most notably, Saturdays are normally part of the established work week, though this has been changing in recent years. Sunday is not a universal day off, so shops and restaurants may have a closing day on any day of the week. Also, the school year is different, based on a school year beginning on April 1st and divided into trimesters separated by vacation periods. On average, Japanese students spend 60 more days in school than Americans, and these vacation times are valued highly. Up until 2002, Japanese students were required to go to school for a half day on Saturday in addition to the full days on Monday to Friday, and older anime may reflect this. However, a good thirty to forty of these days were for school festivals and cultural days. The eighth, fourteenth, fifteenth, twenty-third, and last two days of every lunisolar month are roku sainichi (six fasting days) or Uposatha, the Buddhist version of Sabbath.
For some excellent examples in anime, see Festival Episode and School Festival. Also see the Persona games Persona 3 and Persona 4 if you want to experience a complete Japanese year as a normal highschool student (while fighting The Legions of Hell).